1. Field of Use
This invention relates generally to material chopping devices, such as disc type wood chippers. In particular, it relates to a knife assembly for use therein in which the knife is positionable relative to the knife holding means by positioning serrations and an intermediate land therebetween.
2. Description of the Prior Art
U.S. patent application Ser. No. 187,164 entitled KNIFE ASSEMBLY FOR CHOPPING APPARATUS filed Sept. 15, 1980, by Jack R. Haller and William M. Haselton, issued Sept. 28, 1982 as U.S. Pat. No. 4,351,487 and assigned to the same assignee as the present application discloses a knife assembly for use in a chopping apparatus, such as a wood chipper, of the type having a rotatable disc and an opening therethrough to permit passage of the chopped material through and away from the disc. The assembly comprises a pair of knife holding means including a knife seat and a knife clamp or cover, for engaging a reversible knife with two cutting edges. Means are provided to ensure proper alignment of the knife and its knife holding means. Thus, one of the knife holding means has a flat knife engaging surface for cooperatively engaging a complementary flat surface of the knife. The other knife holding means has either an arcuate protrusion for cooperatively engaging an arcuate groove in the knife, or an arcuate groove cooperating with the groove in the knife to define a space for accommodating a rod which prevents relative blade movement. However, this knife assembly does not permit the position of the knife edge to be adjusted or changed relative to the knife holding means. Such change in position may be necessary after a knife has been sharpened a sufficient number of times to significantly change its dimensions. Or, such change in position might be desirable to alter the size of the chips being cut or to accommodate the nature of the material being cut. Minor adjustments are also desirable to accurately align all adjoining knife edges in a true vertical plane of rotation for closer running clearances between the disc knives and the stationary anvil or base knives, thus producing a product of more uniform size with more cleanly sheared surfaces.
U.S. Pat. No. 3,559,705 issued Feb. 2, 1971, to Louis Salzmann, Jr., for CHIPPER KNIFE AND KNIFE MOUNTING FOR DRUM TYPE WOOD CHIPPER discloses a reversible symmetrical knife for a drum type wood chipper. Such knife is extremely short in length, as compared to the knives used in disc type chippers, and the cutting edge thereof moves in a circular plane, as compared to the flat plane in which the knife cutting edge moves in a disc type chipper. Furthermore, in the structure shown in U.S. Pat. No. 3,559,705 a holder is secured to the inner surface of a drum wall by means of a screw. The head of the holder has a serrated surface which engages the serrated surface of the knife and the knife is secured to the head by means of a screw. In the aforesaid structure, forces acting on the knife as the latter cuts are ultimately transferred as shear forces to the screw through the block and to the other screw through the holder. Although there is a direct transfer of force from the knife to the block and a transfer of force from the knife to the holder through the serrations, there is no direct face-to-face transfer of force from the block to the holder or from the holder to the drum wall. Such an arrangement is tolerable in a drum type chipper wherein the knives are very short but is not acceptable strengthwise in a disc type chipper wherein the knives are quite long and encounter greater forces for a longer time interval during chipping.
U.S. patent application Ser. No. 352,246 entitled DISC TYPE WOOD CHIPPER KNIFE HAVING POSITION ADJUSTING SERRATIONS filed Feb. 25, 1983, by Jack R. Haller and Dino M. Demopoulos, issued Jan. 3, 1984 as U.S. Pat. No. 4,423,758, and assigned to the same assignee as the present application discloses apparatus for chopping material, such as logs. Such apparatus comprises a rotatable disc and at least one radially disposed opening extending through the disc and a knife assembly comprising first knife holding means attached to the disc and adjacent the opening and second knife holding means mounted on the first knife holding means. The first knife holding means comprises a knife seat secured to the disc by screws and a counter knife secured to the knife seat by other screws. The counter knife has a first knife-engaging portion including protruding serrations thereon. The second knife holding means has a second knife-engaging portion including a flat knife-engaging surface. A reversible knife having two cutting edges is mounted between said first and second knife holding means. The knife has a complementary flat surface for cooperatively engaging the flat knife-engaging surface of the second knife holding means. The knife has indented serrations for cooperatively engaging the protruding serrations. Clamping engagement means are provided for clampingly engaging the knife between the counter knife of the first knife holding means and the second knife holding means. The clamping engagement means comprises studs with two ends. Each stud has one of the ends fixed to the second knife holding means and the other of said ends is threaded. The threaded end is threadably engaged to a nut abutting the rotatable disc, whereby rotation of the nut causes axial movement of the stud therealong and permits relative movement between the first knife holding means and the second knife holding means.
The counter knife is secured to said knife seat by securement means, such as the aforesaid other screws, which enables the counter knife to be adjustably positioned relative to the knife seat.
In one embodiment the knife has the same number of indented serrations as there are protruding serrations on the counter knife whereby the knife and the counter knife can assume only one position relative to each other and there is no possibility of knife position error when a knife is installed.
In another embodiment the knife has a larger number of indented serrations when there are protruding serrations on the counter knife whereby the knife and the counter knife can assume a plurality of positions relative to each other to further enhance knife position adjustability.
The serrations disclosed are triangular in cross-section but could take some other form. Knife position gauge means are provided on the inner most end of each knife seat.
A disc type chipper in accordance with U.S. Pat. No. 4,423,758 offers several advantages over the prior art. For example, the configuration and arrangement of the components including the disc, the knife seat, the knife cover, the counter knife and the knife, as well as the cap screws and studs, provides a substantially stronger arrangement than in prior art chippers and provides for transfer of forces between the surfaces of components rather than merely through the studs and cap screws. Furthermore, the knife, when interlockingly engaged with the counter knife, is adjustably positionable in response to positioning of the counter knife on the knife seat, the positioning means therefor including cap screws and shims. In one embodiment, the arrangement of serrations on the knife and counter knife is such that the knife can only assume one position with respect to the counter knife and this arrangement provides for an even range of adjustments of knife positioning. The combination of movement of the knife on the serrations and the fine adjustment of the counter knife by use of shims provides an infinitely adjustable knife projection for very accurate alignment of all adjoining knife edges and subsequent closer running clearance adjustment of the disc knives and the stationary anvils or base knives. In addition, the counter knife serves as the point of maximum wear and, being a relatively small piece, is substantially cheaper to replace when worn than is the larger knife seat in some prior art apparatus.
When the chipper of U.S. Pat. No. 4,423,758 is in operation, the average cutting velocity at the centerline of the knife is approximately 7,000 feet per minute. Rim speed at the periphery of the disc can reach 10,500 feet per minute. The total weight of the rotating mass can reach 21 tons. This combination of great mass plus high velocity makes it imperative that running clearances be maintained and all rotating parts be fastened securely. It is quite common to adjust the chipper so that the running clearance between the disc knives and the base knives is from 0.010" to 0.030".
Knife changing is often done at night by an operator who at best is half asleep and working in a poorly lighted area. Therefore, it is essential to provide a means for locating knives that is as foolproof as possible.
The serrations shown in one embodiment in U.S. Pat. No. 4,423,758 can allow a careless operator to "cross thread" or misalign the grooves or align the male-female grooves in a tip-to-tip position. If the operator then tightens the knife cover stud nuts while the knife is in improper position, he may damage the serration tips and, if he is inattentive, he can mistakenly assume the knife is properly located. Since one can use 3,000 pounds per linear inch as the clamping force to secure the knives, considerable deformation of the serrations can take place.
In practice, a set of 2 or 3 short knives are used to make up a full knife length. If one of the knives in a set is misaligned, it may prevent the other knives in the set from being properly clamped. The same can occur if one of the knives does not receive its full portion of the clamping pressure due to the misalignment of the adjoining knife.
A misaligned knife may eliminate the necessary running clearance, strike the base knives and damage may occur. This may be anything from a broken knife to a severely damaged chipper and injury or death to personnel.